My son, Henry, found this one:
The city of Jerusalem will have twelve gates, three on each of the four sides of the city wall. These gates will be named after the twelve tribes of Israel. The gates of Reuben, Judah, and Levi will be in the north; Joseph, Benjamin, and Dan will be in the east; Simeon, Issachar, and Zebulun will be in the south; Gad, Asher, and Naphtali will be in the west. Each side of the city wall will be two kilometers long, and so the total length of the wall will be ten kilometers. The new name of the city will be “The-Lord-Is-Here!”
Better Bibles Blog 
Does this come from approximating the distances in Greek stadia? Seems maybe if you round each one up and down without reference to the other, you might get something like that.
This is why the US has never adopted the metric system!
Presumably they converted miles into kilometers because 6 miles would normally be thought of as 10km but each side is 1.5 miles which is more than 2km and hence the problem.
As they say, “Do the math!” And you did, Henry. Good job!
Strange as it might seem, the math could be possible. “Two” kilometers does not mean exactly 2, i.e.2.000… kilometers, but more than one-and-a-half and less than two-and-a-half.
Say that each side of the square was 2.49 kilometers, which could be rounded down to two. However, the perimeter would be actually 9.96 kilometers which would be rounded up to ten!